Leighton was also one of nine eyewitnesses who could identify Kodos the Executioner. He and James T. Kirk appeared to have been personal acquaintances, perhaps as a result of their shared experiences on Tarsus IV.
In 2266, he diverted the USS Enterprise to Planet Q, ostensibly to confirm his discovery of a new synthetic food that could totally end the threat of famine on Cygnia Minor, a nearby colony. In fact, he diverted the Enterprise because he believed Anton Karidian, a traveling performer, was actually Kodos. He hoped Kirk, another of the eyewitnesses, would help him in his quest to bring Kodos to justice. Kirk wasn't convinced until, ironically, Leighton was found dead. Lenore Karidian, insanely desperate to protect her father from his past, had murdered Leighton; he was the seventh victim of her quest to eliminate all those who could identify Kodos. He was survived by his wife Martha Leighton. (TOS: "The Conscience of the King")